Gemini 7

NSSDCA/COSPAR ID: 1965-100A

Description

Gemini 7 was the fourth crewed Earth-orbiting spacecraft of the Gemini
series, having been launched before Gemini 6A. It carried astronauts
Frank Borman and Jim Lovell on the 14 day mission. Its mission priorities
were (1) to demonstrate a 2-week flight, (2) to perform stationkeeping
with the Gemini launch vehicle stage 2, (3) to evaluate the 'shirt
sleeve' environment and the lightweight pressure suit, (4) to act as a
rendezvous target for Gemini 6, and (5) to demonstrate controlled reentry
close to the target landing point. The crew members had three
scientific, four technological, four spacecraft, and eight medical
experiments to perform.

Mission Profile

Gemini 7 was launched from Complex 19 at 2:30:03 p.m. (2:30:03.702 UT) on 4 December 1965
and inserted into a 161.6 x 328.2 km orbit at 2:36:11. Immediately
after separation Gemini 7 began stationkeeping operations with the Titan
II second stage at distances from 6 meters to 80 km over a period of 17
minutes. On the third revolution the perigee was raised to 230 km to
ensure an orbital lifetime of 15 days. On 6 December, 45 hours into the
mission, Lovell removed his spacesuit to evaluate the shirtsleeve
environment. The first five days were spent conducting experiments and
spacecraft tests. On 9 December the orbit was circularized to 299.7 x
303.7 to prepare for the rendezvous exercise with Gemini 6A. On 10
December 140 hours into the mission Lovell put his suit back on and
Borman removed his. Some 20 hours later Lovell removed his suit as well
and both astronauts operated without suits for the remainder of the mission except for the rendezvous with Gemini 6A and reentry.

Experiments were conducted over the next few days and on 15 December
Gemini 6A was launched. Gemini 6A caught up to Gemini 7 and rendezvous
was technically achieved and stationkeeping begun on 15 December at
2:33 p.m. EST with the two Gemini spacecraft in zero relative motion at
a distance of 110 meters. Stationkeeping maneuvers involving the
spacecraft circling each other and approaching and backing off
continued for 5 hours 19 minutes over three and a half orbits. During
the maneuvers, all four astronauts on both spacecraft took turns in the
formation flying activities and photographs were taken from both
spacecraft. This marked the first time two spacecraft were maneuvered with respect to each other by their crews. At the end of stationkeeping Gemini 6A fired thrusters to move to a position roughly 50 km away from Gemini 7 for drifting flight during the sleep period. Gemini 6A
returned to Earth on December 16. Gemini 7 remained in Earth orbit and
reentered two days later.

Retrorockets were fired at the end of revolution 206 on 18 December at
8:28:07 a.m. to begin the reentry sequence. Splashdown followed at
9:05:04 in the western Atlantic southwest of Bermuda at 25.42 N, 70.10 W,
only 12.2 km from the target point. The astronauts were recovered by
helicopter and brought aboard the aircraft carrier U.S.S. Wasp at 9:37.
The spacecraft was recovered at 10:08. Total mission elapsed time was
330:35:01, making this the longest anyone had ever stayed in space. The
astronauts were pronounced in "better than expected" physical condition
after their two week flight.

All primary mission objectives were successfully completed. The three scientific experiments: synoptic terrain photography, synoptic weather photography, and visual acuity in the space environment were all
completed successfully. All other onboard experiments were performed
except landmark contrast measurement and star occultation navigation,
due to equipment failure. Only partially completed were in-flight
sleep analysis, proton-electron spectrometer, and optical communication.
Minor malfunctions related to fuel cells and attitude control thruster
occurred but did not hamper the mission.

Spacecraft and Subsystems

The Gemini spacecraft was a cone-shaped capsule consisting of two components, a reentry module and an adaptor module. The adaptor module made up the base of the spacecraft. It was a truncated cone 228.6 cm high, 304.8 cm in diameter
at the base and 228.6 cm at the upper end where it attached to the base of the
reentry module. The re-entry module consisted of a truncated cone which
decreased in diameter from 228.6 cm at the base to 98.2 cm, topped by a short
cylinder of the same diameter and then another truncated cone decreasing to a
diameter of 74.6 cm at the flat top. The reentry module was 345.0 cm high,
giving a total height of 573.6 cm for the Gemini spacecraft.

The adaptor module was an externally skinned, stringer framed structure, with magnesium stringers and an aluminum alloy frame. The adaptor was composed of two parts, an equipment section at the base and a retrorocket section at the top.
The equipment section held fuel and propulsion systems and was isolated from the
retrorocket section by a fiber-glass sandwich honeycomb blast shield. The
retrorocket section held the re-entry rockets for the capsule.

The reentry module consisted mainly of the pressurized cabin which held the two Gemini astronauts. Separating the reentry module from the retrorocket section of
the adaptor at its base was a curved silicone elastomer ablative heat shield.
The module was composed predominantly of titanium and nickle-alloy with beryllium
shingles. At the narrow top of the module was the cylindrical reentry control
system section and above this the rendezvous and recovery section which holds the
reentry parachutes. The cabin held two seats equipped with emergency ejection
devices, instrument panels, life support equipment, and equipment stowage
compartments in a total pressurized volume of about 2.25 cubic meters. Two large
hatches with small windows could be opened outward, one positioned above each seat.

Control, Propulsion, and Power

Attitude control was effected by two translation-maneuver hand controllers, an attitude controller, redundant horizon sensor sytems, and reentry control electronics, with guidance provided via an inertial measuring unit and radar system. The orbital attitude and maneuver system used a hypergolic propellant combination of monomethylhydrazine and nitrogen tetroxide supplied to the engines
by a helium system pressurized at 2800 psi. Two 95 lb translation thrusters and
eight 23 lb attitude thrusters were mounted along the bottom rim of the adaptor,
and two 79 lb and 4 95 lb thrusters were mounted at the front of the adaptor.
Power was supplied by a fuel cell power system to a 22- to 30-volt DC two-wire
system. During reentry and post-landing power was supplied by four 45 amp-hr
silver-zinc batteries.

Communications

Voice communications were performed at 296.9 MHz with an output power of 3 W. A
backup transmitter-receiver at 15.016 MHz with an output power of 5 W was also
available. Two antenna systems consisting of quarter-wave monopoles were used.
Telemetry was transmitted via three systems, one for real time telemetry, one for
recorder playback, and a spare. Each system was frequency-modulated with a minimum
power of 2 W. Spacecraft tracking consisted of two C-band radar transponders and
an acquisition-aid beacon. One transponder is mounted in the adaptor with a peak
power output of 600 W to a slot antenna on the bottom of the adaptor. The other is
in the reentry section, delivering 1000 W to three helical antennas mounted at 120
degree intervals just forward of the hatches. The acquisition-aid beacon was
mounted on the adaptor and had a power of 250 mW.

Reentry

At the time of reentry, the spacecraft would be maneuvered to the appropriate orientation and equipment adaptor section would be detached and jettisoned, exposing
the retrorocket module. The retrorockets consisted of four spherical-case
polysulfide ammonium perchlorate solid-propellant motors mounted near the center of
the reentry adaptor module, each with 11,070 N thrust. They would fire to initiate
the spacecraft reentry into the atmosphere, with attitude being maintained by a
reentry control system of 16 engines, each with 5.2 N thrust. The retrorocket
module would then be jettisonned, exposing the heat shield at the base of the reentry
module. Along with the ablative heat shield, thermal protection during reentry was provided by thin Rene 41 radiative shingles at the base of the module and beryllium
shingles at the top. Beneath the shingles was a layer of MIN-K insulation and
thermoflex blankets. At an altitude of roughly 15,000 meters the astronauts would
deploy a 2.4 meter drogue chute from the rendezvous and recovery section. At 3230
meters altitude the crew releases the drogue which extracts the 5.5 meter pilot
parachute. The rendezvous and recovery section is released 2.5 seconds later,
deploying the 25.6 meter main ring-sail parachute which is stored in the bottom of
the section. The spacecraft is then rotated from a nose-up to a 35 degree angle for
water landing. At this point a recovery beacon is activated, transmitting via an HF
whip antenna mounted near the front of the reentry module.

Gemini Program

The Gemini program was designed as a bridge between the Mercury and Apollo programs,
primarily to test equipment and mission procedures in Earth orbit and to train
astronauts and ground crews for future Apollo missions. The general objectives
of the program included: long duration flights in excess of of the requirements of
a lunar landing mission; rendezvous and docking of two vehicles in Earth orbit;
the development of operational proficiency of both flight and ground crews; the
conduct of experiments in space; extravehicular operations; active control of
reentry flight path to achieve a precise landing point; and onboard orbital
navigation. Each Gemini mission carried two astronauts into Earth orbit for
periods ranging from 5 hours to 14 days. The program consisted of 10 crewed
launches, 2 uncrewed launches, and 7 target vehicles, at a total cost of
approximately 1,280 million dollars.